Ormocer-matrix composites can exhibit sufficient viscoelastic stability

Objectives: To compare the creep behaviour between a series of TEGMA-free Ormocer matrix composites with classical BisGMA/TEGMA matrix composites at different levels of filler-fraction.

Methods: Three Ormocer matrix composites with descending levels of filler-fraction; 86, 79 and 69%w/w were evaluated versus approximately similar filler loading of BisGMA/TEGMA matrix composites. Three cylindrical specimens (4mm x 6mm) per material were prepared using steel moulds with thorough light curing from multiple directions at 600mW/cm². All specimens were stored for a week in water at 37ºC. A creep measurement apparatus was used to determine the creep-strain and recovery. Constant compressive stress of 36MPa was applied to each specimen for 2 h followed by load-removal, for 2 h of strain-recovery. Axial-strain measurements were obtained continuously over the total of 4 h. One-way ANOVA and an independent T-test were applied.

Results:

Maximum creep-strain (%)

Resin System & Filler-Load w/w	69%	79 %	86 %
Ormocer matrix composite Mean(S.D)	5.44 (0.07)	4.08 (0.57)	1.96 (0.27)
BisGMA/TEGMA matrix composite Mean(S.D)	3.63 (0.10)	2.07 (0.14)	1.59 (0.26)

At lower filler-fractions Ormocer matrix composites showed greater maximum creep-strain (%) compared to the control BisGMA/TEGMA matrix composites (p<0.05). However there was no significant difference between these resin systems at the higher filler fraction (p> 0.05).

Conclusion: Grandio materials showed lower maximum creep-strain than Ormocer materials. Both materials showed an increase in creep resistance when filler-fraction was increased.